RFE Proposal Set Operations - RFC
Greetings, this is a proposal for a Request for Enhancement in the JDK. It
is posted here for the review and comment. Basically an RFC on a RFE. =)
Please indicate your comments on the matter.
The proposal is to have a set of operations for perfomring Non-destructive
mathematical set operations on collections. Additionally, the addition of
set operations to rename the old operations int java.util.Collection
interface to names that are mathematically accurate; so that
removeAll(Collection c) would have an alias of difference(Collection c) and
retainAll(Collection c) would have a alias of intersection(Collection c).
The following methods would be added to the java.util.Collections class.
/**
* Performs the non-descturctive union of two collections.
* The resulting collection is the union of the two collections with no
duplicates.
* @author Robert Simmons Jr.
* @param a The first collection of objects.
* @param b The second collection of objects.
* @return The collection wise union of and b.
*/
publicfinalstatic Collection collectionUnion(final Collection a,final
Collection b){
Collection results =new HashSet(a);
Iterator iter = b.iterator();
while (iter.hasNext())
results.add(iter.next());
return results;
}
/**
* Performs the intersection of two collections.
* The resulting collection is the intersection of the two collections with
no duplicates.
* @author Robert Simmons Jr.
* @param a The first collection of objects.
* @param b The second collection of objects.
* @return The collection wise intersection of a and b.
*/
publicfinalstatic Collection collectionIntersection(final Collection a,
final Collection b){
Collection results =new HashSet();
Iterator iter = a.iterator();
Object element =null;
while (iter.hasNext()){
element = iter.next();
if (b.contains(element)) results.add(element);
}
return results;
}
/**
* Performs the difference of two collections.
* Removes all elements from a that appear in b.
* @author Robert Simmons Jr.
* @param a The first collection of objects.
* @param b The second collection of objects.
* @return The collection wise difference of b elements removed from a.
*/
publicfinalstatic Collection collectionDifference(final Collection a,
final Collection b){
Collection results =new HashSet(a);
Iterator iter = b.iterator();
while (iter.hasNext())
results.remove(iter.next());
return results;
}
/**
* Performs the XOR union of two collections.
* The resulting collection is the union of the two collections with objects
that appear in
* a and b left out.
* @author Robert Simmons Jr.
* @param a The first collection of objects.
* @param b The second collection of objects.
* @return The collection wise union of a and b excluding any objects that
appear in both a and b.
*/
publicfinalstatic Collection collectionXORUnion(final Collection a,final
Collection b){
Collection results =new HashSet(a);
Iterator iter = b.iterator();
Object element =null;
while (iter.hasNext()){
element = iter.next();
if (!(b.contains(element))) results.add(element);
}
return results;
}
/**
* Performs the union of two maps.
* The resulting map is the union of the two maps with no duplicates.
* When working with set operations on a map, the set is assumed to be the
key set. For
* this reason, if both sets have the same key but different values then the
value from
* set b will beused as the value.
* @author Robert Simmons Jr.
* @param a The first map of objects.
* @param b The second map of objects.
* @return The map wise union of and b.
*/
publicfinalstatic Map mapUnion(final Map a,final Map b){
Map results =new HashMap(a);
Iterator iter = b.keySet().iterator();
Object key =null;
while (iter.hasNext()){
key = iter.next();
results.put(key, b.get(key));
}
return results;
}
/**
* Performs the intersection of two maps.
* The resulting map is the intersection of the two maps with no duplicates.
* When working with set operations on a map, the set is assumed to be the
key set. For
* this reason, if both sets have the same key but different values then the
value from
* set b will beused as the value.
* @author Robert Simmons Jr.
* @param a The first map of objects.
* @param b The second map of objects.
* @return The map wise intersection of a and b.
*/
publicfinalstatic Map mapIntersection(final Map a,final Map b){
Map results =new HashMap();
Iterator iter = a.keySet().iterator();
Set bKeys = b.keySet();
Object key =null;
while (iter.hasNext()){
key = iter.next();
if (bKeys.contains(key)) results.put(key, b.get(key));
}
return results;
}
/**
* Performs the difference of two maps.
* Removes all elements from a that appear in b.
* In this case, the set is determined to be the set of keys. The set of
keys from
* b will be used to remove keys from a.
* @author Robert Simmons Jr.
* @param a The first map of objects.
* @param b The second map of objects.
* @return The map wise difference of b elements removed from a.
*/
publicfinalstatic Map mapDifference(final Map a,final Map b){
Map results =new HashMap(a);
Iterator iter = b.keySet().iterator();
while (iter.hasNext())
results.remove(iter.next());
return results;
}
/**
* Performs the XOR union of two maps.
* The resulting map is the union of the two maps with objects that appear
in
* a and b left out.
* When working with set operations on a map, the set is assumed to be the
key set. For
* this reason, if both sets have the same key but different values then the
value from
* set b will beused as the value.
* @author Robert Simmons Jr.
* @param a The first map of objects.
* @param b The second map of objects.
* @return The map wise union of a and b excluding any objects that appear
in both a and b.
*/
publicfinalstatic Map mapXORUnion(final Map a,final Map b){
Map results =new HashMap();
Iterator iter = a.keySet().iterator();
Set bKeys = b.keySet();
Object key =null;
while (iter.hasNext()){
key = iter.next();
if (!(bKeys.contains(key))) results.put(key, b.get(key));
}
return results;
}
Transcript of mail session with Sun java developer after bug submission:
Hi Robert Simmons Jr.,
Thank you for the feedback.
The method names in java.util.Set conform to the parent interface,
java.util.Collection. As for the destruction situation, returning a new set
also would involve creating and populating a new set.
If you would like to pursue this Request for Feature Enhancement (RFE)
further,
I would suggest that you first post this idea to a newsgroup and request
comment from other Java developers. The issues that we have discussed are a
good starting point.
You can view a list of Java newsgroups at:
http://java.sun.com/aboutJava/newsgroups.html
Based on the responses, please feel free to submit a new RFE containing a
link to the newsgroup. Thank you for your time.
Regards,
Jonathan
"Simmons, Robert" wrote:
>
> I understand your reply now. However I put it to you that the names of
these
> operations are HORRIBLY named. They should be named according to the
> mathematical operations. Further, they are destructive to the set being
> checked and I dont want that. The set operations should give me back a set
> and not destroy the current set. If they destroy the current set then I
have
> to spend time copying the thing before I run the set operation which is
> truly not performant. Do an intersection of 400,000 elements with another
fo
> 300,000 elements and you have to first copy one and then the retain all
> method has to iterate through the entire set. This is very bad logic. In
the
> code I gave you, you have to only iterate through the set and not copy it.
>
-- Original Bug Report-
category : java
release : 1.4
subcategory : classes_util
type : rfe
synopsis : java.util.Collections Class Should Implement Logical Set
Operations
description : FULL PRODUCT VERSION :
This issue is pertinent to all java versions including the new 1.4 version.
FULL OPERATING SYSTEM VERSION : Occurs in all operating
Systems.
ADDITIONAL OPERATING SYSTEMS : NA
A DESCRIPTION OF THE PROBLEM :
The java.util.Collections class is a class that is used to
manipulate sets and change them into various forms. Missing
from this is a feature that would define set operations,
such as Union, Intersection, and so on on the sets. This
would be extremely beneficial. I have written an extension
to this class that does just that and would like to submit
it for donation. All I ask is that the javadoc tag naming
me as author be retained.
This bug can be reproduced always.
- BEGIN SOURCE -
<!-- snip source .. see above -->
- END SOURCE -
CUSTOMER WORKAROUND :
Writing your own classes to do this, however it is so basic
that it should be in there.
workaround :
suggested_val :
cust_name : Robert Simmons Jr.
cust_email : robert.simmons@ingenium-ag.com
jdcid : Derisor (old one was gnuish)
keyword : webbug
company : Ingeniums Pharmaceuticals AG
hardware : x86
OSversion : Linux
bugtraqID : 0
dateCreated : 2002-03-11 13:31:18.3
dateEvaluated : 2002-04-11 18:08:17.247
--
Robert Simmons Jr.
Senior Software Engineer
Ingenium Pharmaceuticals, Munich Germany.
-
--
Robert Simmons Jr.
Senior Software Engineer
Ingenium Pharmaceuticals, Munich Germany.
-
--
Robert Simmons Jr.
Senior Software Engineer
Ingenium Pharmaceuticals, Munich Germany.
-
